1. Field of the Invention
The present invention relates to a multi-spindle head-replacing type machine tool comprising a machining unit disposed on a base for advancing and retreating movements between an original position and a machining position, a first annular guide rail including a movable rail integral with the machining unit and a stationary rail to surround the machining unit which is located in the original position, a second annular guide rail disposed concentrically with and at a place axially offset from the first guide rail, a plurality of multi-spindle heads travellably carried on each of the first and second guide rails, first and second index mechanism releasably connected respectively to the multi-spindle heads on the first and second guide rails for driving such multi-spindle heads for angular displacement, and an elevator mechanism disposed sideways from the first and second guide rails at a place offset from the movable rail for providing replacement of the multi-spindle heads between the first and second guide rails.
2. Description of the Prior Art
Such multi-spindle head-replacing type machine tool is conventionally known from Japanese Patent Publication No. 13923/86.
With the above conventional machine tool, however, a lift mechanism and a shift mechanism are required for transferring of a multi-spindle head between the first and second guide rails and the elevator mechanism, resulting in a complicated construction. In addition, a space must be left in the second guide rail for replacement of the multi-spindle, resulting in a correspondingly decreased amount of multi-spindle heads stored.